1. Field of the Invention
The present invention relates to a method and an apparatus for measuring photoluminescence in crystal such as silicon.
2. Related Background Art
The photoluminescence measuring method is one of methods for measuring a distribution of defects in a crystal. When a silicon (Si) crystal is an object, an Ar (488,514 nm) laser or a He--Ne (633 nm) laser is used in the photoluminescence method. FIG. 1 shows a conventional photoluminescence measuring apparatus in which the Ar or He--Ne laser is projected toward an object and fluorescence generated in the object is spectroscopically measured through a microscope. The Ar or He--Ne laser beam is projected in the horizontal direction, then reflected at 90 degrees by a half mirror 1, and focused on an object 3 through an objective lens. The projected laser beam excites luminescent centers, which will fluoresce. The fluorescence light passes through the half mirror and forms an image through an image forming lens 11 on a pin hole or slit 5 provided on a spectroscope 4. The fluorescence light is then diffracted by a diffraction grating 6 disposed inside the spectroscope 4 to be guided onto a light receiving element 7, being distributed on the element in accordance with its frequency distribution. A control computer 8 analyzes the image received by the light receiving element while controlling a stage controller 9 to move the object 3 two-dimensionally, so as to show a distribution of generated fluorescence on a display.
It is important to measure a life time of luminescence center in the photoluminescence method. A general measurement of life time is such that a projection beam is supplied from a pulse laser source or pulse light source and that a damping of fluorescence produced under irradiation with the pulse beam is evaluated, as shown in FIG. 2. There is another method for measuring the life time, in which a semiconductor laser beam is input as excitation energy and a damping of exciton is observed by microwave.
There are other conventional techniques concerning the photoluminescence method for example as described in Japanese Patent Application No. 54-109488 and Japanese Laid-open Patent Application No. 62-119446, in which a scattering image or a fluorescence image of defect is obtained using a laser beam. Also, Japanese Patent Application No. 60-53368 describes a method to obtain a scattering image of defect in silicon crystal under irradiation with YAG laser. Additionally, reference is made to K. Moriya and T. Ogawa, Jpn. J. Appl. Phys., 22 (1983)L207 describing related art.